A composite coating using mixed powders of pure Al and α-Al2O3 as feedstock was deposited on AZ91D alloy substrate by cold spraying. The content of α-Al2O3 in mixed powders was 50wt%. Electrochemical experiments were carried out using 3.5wt.% NaCl solution as electrolyte. Because of dense structure, the composite coating could separate substrate from electrolyte thoroughly for long time immersion. The corrosion behavior of the composite coating was evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. It is found that the composite coating presented much better corrosion resistance than bare AZ91D alloy, even than bulk 1050 aluminum by electrochemical studies in 3.5wt.% NaCl solution.